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However, Dr de Wert said he believed that there might be an argument for making human cloning legal if it could be made safe.

"It could be used, in principle, to treat some types of infertility, for instance, when a man is unable to produce any germ cells in his sperm."

One reason why clones are at risk of genetic damage is that they are created from adult cells that may have acquired DNA mutations and damage as they grow older in their hosts' bodies.

Dr Severino Antinori, who runs a fertility clinic in Rome, has announced plans to clone a baby within a year. This week Prof Hans Evers, the new head of the European Society of Human Reproduction and Embryology, accused him of "irresponsibly" raising the hopes of infertile couples.

Dr Judith Gianotten, of the Amsterdam Academic Medical Centre, told the conference that her team of scientists had discovered two mutated genes passed from mothers to sons that were linked to male infertility.

The mutations helped to explain why some men had such low sperm counts and could offer new targets for fertility treatments, she said.

Her team took DNA from 77 men with low counts and compared it with DNA from 65 fertile men. Two mutated genes were found in four of the sub-fertile men.

She said:"The fact that the mutations in the genes appear to be inherited from the mother explains how sub-fertility from impaired sperm production can be passed on to the next generation. If they were from the father, the mutations would become extinct."

Girls with Turner's syndrome, a genetic condition that leaves women infertile, may be able to have children in the future, the conference heard.

Scientists found that some teenage girls with the disease had undeveloped eggs in their ovaries that could be removed and frozen for future use.

Turner's syndrome affects one in 3,000 girls. They are born with one X chromosome instead of two and normally their ovaries fail to develop.

It is thought that they are born with primordial follicles - the cells that develop into eggs - in their ovaries, but that they start to disappear soon after birth.

Although about a third of girls with the syndrome show some sexual development at puberty, Turner's syndrome women are usually infertile. Only one in 20 are able to conceive naturally.

Julius Hreinsson, an embryologist at Huddinge University Hospital in Sweden, has obtained ovarian tissue containing follicles from five girls.

"To our knowledge this is the first time that follicles have been observed in ovarian tissue from patients with Turner's syndrome," he said. "Our findings give hope for the future infertility treatment of these girls."